Under a variety of weather conditions such as rain, sleet, hail or snow, the wings of an aircraft may be subject to the formation of ice on the wing surface which can be a severe hazard to navigation. Such an ice layer, if undetected, can cause an aircraft to go off course, or worse, result in an airplane crash particularly during take-offs or landings. The accurate detection of the formation of a layer of ice on airplane wings is thus a crucial element in safe air travel.
Various devices are known that have been used to monitor the development of a layer of ice on aircraft wings. For example, U.S. Pat. No. 4,604,612 (Watkins et al.) discloses a method of detecting ice formation utilizing two ultrasonic transducers spaced apart from each other wherein the second transducer is adapted to detect propagation of an ultrasonic wave from the first. This device operates at relatively low frequencies in the range of 250 Khz to 1 Mhz. The sensitivity of this device, which is inversely dependent on frequency, will thus not be as acute as in those devices having a much higher frequency. Another known device, as disclosed in U.S. Pat. No. 4,461,178 (Chamuel), also detects wing icing by monitoring variations in flexural waves transmitted through the outer plate material of an aircraft airfoil.
Recently, it has been found that acoustic wave devices utilizing a shear horizontal acoustic plate mode can yield a wealth of information regarding liquid-solid interfaces. Information regarding the viscosity of the liquid, the mass of solid films bound to the crystal surface under the liquid, the density of chemical species bound to the crystal surface, and the electrical properties of the liquid to be detected can all be obtained using those devices. It would be desirable, therefore, to develop a method and device for utilizing a shear horizontal acoustic plate mode which can be used to study the physical chemistry of liquid-solid phase transitions in general, and to provide a means by which icing conditions such as those that would occur on the wings of an aircraft could be monitored.